A sea otter-shaped rubble pile in space

True to its name, the Japanese spacecraft Hayabusa, which means "falcon" in Japanese, hovered over the near-Earth asteroid Itokawa last fall, taking up-close measurements and photographs. Then it swooped down for a brief landing and the first-ever sample attempt on an asteroid.

The findings from this space mission, being published in the June 2, 2006 issue of the journal Science, will help researchers understand the structure and composition of the "near-Earth asteroids" that periodically whiz past our planet.

Asteroid Itokawa, named after Japanese rocket scientist Hideo Itokawa, was chosen as Hayabusa's "prey" in part because it is one of the most common types of rocky near-Earth asteroids. The relatively tiny asteroid is only 500 meters long.

Some of the photographs taken by Hayabusa's camera even show the spacecraft's shadow, revealing how close the spacecraft came to the asteroid during its hover.

Akira Fujiwara of the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA) and his colleagues report that asteroid Itokawa has two parts, a smaller "head" and larger "body," giving it the shape of a sea otter.

It appears to consist of rubble, which is interesting because previously studied asteroids generally appear to be lumps of solid rock.

The rubble is very loosely packed and porous, just barely held together by the asteroid's own gravity. If an object collided with Itokawa, it would probably be like a rock landing in a bucket of sand. The signs of impacts with small space rocks get erased as the rubble shifts after the impact, so there are very few craters on Itokawa.

Hayabusa is also an important mission because it was designed to take samples from its destination and return them to Earth. The spacecraft attempted to collect some of the asteroid's material in a capsule, in order to bring it back to Earth, but this effort may not have been successful.

The spacecraft, now low on fuel, is slowly gliding back to Earth, where it may drop its cargo capsule into the Australian desert in 2010.

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This article is being published in the June 2, 2006 issue of the journal Science